Otitis media (OM) is one of the major causes of morbidity and the most common cause of hearing loss in children. Eighty percent of the children born each year experience at least one episode of OM by their third birthday, and one in three have repeated bouts of the disease. OM has an annual cost of $5 billion and accounts for an estimated 31 million annual visits to the doctor's office. Due to the rapid worldwide increase in antibiotic resistance among OM pathogens there is now an urgent need to develop new and innovative non-antibiotic approaches to prevent and manage this disease. To this end, it is imperative to understand how the molecules of the innate (natural) immune system function and protect the tubotympanum before the activation of adaptive immunity. We hypothesize that the tubotympanum is protected by an highly effective innate immune system, including the secreted antimicrobial innate immune molecules, such as lysozyme, latoferrin, B-defensins, and surfactant proteins A and D (SP-A and SP-D). We further hypothesize that innate immune molecules can act synergistically to maximize their anti-microbial activities against pathogens and that their immaturity or poor function is a risk factor for OM. Our long-term goal is to elucidate the role of innate immunity in OM pathogenesis and to develop novel preventative and therapeutic measures. Towards our objective, we will: 1) determine the individual and synergistic bacteriostatic and bactericidal activities of the innate immune molecules against the major OM pathogens - nontypable H. influenzae (NTHi), S. pneun2oniae and M. catarrhalis; 2) determine the in vivo time course of changes in the expression of innate immune molecules in the rat middle ear in response to inactivated NTHi; 3) identify the intracellular signal transduction cascade(s) that result in the activation of the innate immune molecules; 4) determine the role of the anti-microbial surfactant proteins, SF-A and SP-D, in OM using knock out mice for these molecules.